Thursday has been a big day for central bank intervention. The European Central Bank lowered its key interest rate by a quarter percentage point to 0.75%. The Bank of England decided to flood the market with British pounds through quantitative easing, increasing asset purchases by £50 billion ($78.1 billion).

The People's Bank of China also cut several key interest rates for the second time in less than a month, bringing its lending rate down by 0.31 percentage point to 6%.

Rate cuts by so many central banks are likely to give markets a temporary boost, said Mark Helweg, president of financial software maker MicroQuant. But given that interest rates have been pushed to record lows, Helweg warned investor confidence could be shaken if it looks like central banks are running out of ideas.

"If they fail to hold those gains, all this could be perceived as a negative," he said. "What else can central banks do? Where else can they go?"

Meanwhile, Spain sold €3 billion ($3.8 billion) in 3- and 10-year bonds Thursday -- the first auction since last week's eurozone summit. Yields on the 10-year bond moved up to 6.54% but stayed below peak levels hit in June.

On the domestic front, investors head into Thursday with the U.S. labor market in focus.

First-time unemployment claims for the week that ended June 30 came in at 374,000, down 14,000 from the prior week. The Labor Department's figures were just below economists' expectations.

The ADP report could raise expectations of Friday's government jobs report for June. Analysts surveyed by CNNMoney expect that the U.S. economy added just 80,000 jobs last month.

The morning started on a positive note as planned job cuts fell in June to a 13-month low of 37,551 job cuts. The figure is lower than last month's numbers and 9.4% below what it was in June last year, according to global outplacement consulting firm Challenger, Gray & Christmas.

U.S. stocks rallied on a holiday-shortened trading day Tuesday, as investors reacted to strong auto sales and an increase in factory orders for May. U.S. markets were closed Wednesday for Independence Day.

Economy: A purchasing managers' survey of the services sector in June is due at 10 a.m. ET from the Institute for Supply Management. The index is expected to come in at 53, down from 53.7 in May. Any reading above 50 signals expansion.

Currencies and commodities: The dollar rose against the euro and British pound, but lost ground against the Japanese yen.